Reading/writing audio information on magnetic strip usually takes place using a tape-supporting the strip and wound on a reel and, as reading/writing means, a magnetic head positioned close to the tape which moves below it at a uniform speed, drawn by appropriate motor means which ensure the alignment of the tape below the head and the uniformity of the relative movement.
The uniformity of the movement is an essential requirement, and is a critical factor.
If this is not so the audio playback is distorted in an annoyingly noticeable manner while, conversely, errors of alignment and variations in the angular orientation of the air gap of the magnetic head with respect to the magnetic track both during recording and reading are much less noticeable on playback, translating into an attenuation of the signal read (which may largely be compensated for with systems for automatic gain control, thus controlling the volume), and a limitation of the frequency response, perceptible only to the most refined ear.